Circular knitting machines consist generally of one or two needle cylinders 1 which, as shown in FIG. 1, comprise tricks 2 in their outer cylindrical surface. The tricks represent the guides for the needles 3 which during their vertical travel form the stitch loops in cooperation with the sinkers.
The number of tricks is equal to the number of needles which slide within them with reciprocating motion by the effect of raising and lifting cams not shown in FIG. 1. Generally, in hosiery machines the number of tricks and needles is between 200 and 400. The cylinder is rotated and with it there rotate the needles which during their reciprocating movement are fed with yarn in fixed angular positions when in their highest point of travel by yarn feed stations consisting of one or more yarn guides which are selectively presented to the needle hooks so that they seize the yarn from them.
To produce hosiery articles generally only a fraction of the available needles are used at the same time and in the same manner, except for the plain knitwork parts, for which all the needles are operated between their maximum and minimum level, all being fed with yarn at each knitting course, and all being moved in the same manner.
When the machine is not producing plain knitwork, in order to produce other types of knitwork some needles are required to produce stitch loops and therefore be raised to the maximum level at the feed station in order to seize the yarn, while others have to be raised to an intermediate level to take up yarn without clearing the previous stitch in order to form a tuck stitch, or have to be raised with a certain delay so that they do not seize the yarn fed in that feed station and therefore do not form new loops with it. In other words a needle selection has to be made. This means that before each feed it has to be determined which and how many needles must undergo a certain travel and which and how many other needles must undergo a certain different travel or indeed undergo no travel.
With reference to FIG. 1, in the known art this selection is effected by the jacks 4 which slide in the same tricks 2 as the needles lying above them, to urge the needles upwards and move them to a higher level in order to seize the yarn. After seizing the yarn the needles are controlled in their reciprocating movement by their own cams and counter-cams which are fixed relative to the cylinder, and which are not shown in FIG. 1 but are shown in the subsequent figures.
FIG. 1 shows an elastic jack 4, able to radially flex its lower end. When the jacks 4 have moved the needle into its working position they withdraw from the needle butt and return downwards. If the needle, after completing its task of seizing the yarn and forming the stitch loop and therefore being at its minimum level, is not required to seize a further yarn from another feed it remains at this level until its control jack or other machine members move it upwards again.
The shank of the jack 4 comprises in its middle part a projection 5, i.e. the upper guide butt, which comes into engagement with its own control cam 6 for urging the jack downwards when it has completed its task of raising the needle 3. Proceeding downwards along the jack shank there is a lower butt 7 which comes into engagement with the cam ring 8 provided with a raising contour 9 which raises the jack together with its overlying needle, this thus being selected to seize the yarn, and with a contour 10 which with its inner face engages the vertical face of the butt 7 to urge the foot of the elastic jack 4 into the interior of the trick 2. When in this position of approach to the interior, the butt 7 is unable to engage the raising contour 9 of the ring 8 and the jack remains lowered. The lowering cams 6 and the raising and approach contours 9 and 10 are obviously offset angularly and operate at different times on each jack.
In circular knitting machines, needle selection is generally conducted by maintaining those jacks corresponding to the needles to be raised by the raising butt in a position withdrawn outwards to cause them to engage the raising contours, while maintaining those jacks corresponding to the needles not to be selected in their position of approach to the interior of the trick, whether elastic jacks or conventional rigid jacks are used.
When elastic jacks are used, they tend spontaneously to move their lower butt 7 outwards to engage the raising contour 9 and be raised, whereas with conventional jacks their approach and withdrawal are effected by suitably positioned cams fixed relative to the cylinder.
The jacks 4 are maintained in position so that the flexure or displacement of their lower part does not cause their upper part to escape from the trick, this being achieved for example by one or more circular springs 12 rigid with the cylinder and surrounding their upper part. They are held in position by circumferential grooves in the cylinder, so that the springs lie internal to the face of the needle cylinder 1.
In FIG. 1 the selection device, indicated schematically by 11, can either allow the jack 4 to move outwards and rise on the cam 9, or can urge it into its trick so that it remains low. Conventional selection uses mechanical selectors acting on a series of intermediate butts, but this type of selection has considerable limits in terms both of operation and of the number of possible selections.
The most recent machines use electromagnetic selection devices which allow a greater selection speed and a greater number of programmable selections, with advantages in terms of machine productivity and the greater variety of possible patterns.
These selection devices are divided essentially into two categories, namely fixed devices which do not rotate with the cylinder and are positioned to precede each feed station, and to which the jacks are presented in sequence as they rotate, and selection devices which rotate together with the cylinder (and with its jacks) and which are therefore always positioned at the jacks and can act on them at any moment, rather than only during the very short time in which the jack passes in front of them. This second type of selection is also effected before the jacks pass in front of the feed stations, but there is greater freedom with regard to the requirements of synchronization and the constraints on the time available for the selection, however a larger number of selection actuators are required, these being equal in number to the number of needles rather than to the number of feed stations. Needle selection devices and methods of the two described types, operating on both rigid and elastic jacks, are described in European Patent Applications Publication Nos. 0379234, 0431674, 0441005, 0479371 and Italian patent Application N. 22172 A/90 of the present applicant.
Those methods which use jacks in circular knitting machines for needle selection involve a selection linkage which is complicated and requires a cylinder 1 of sufficient length to contain the needles 3, the jacks 4 and possibly vertical selection actuators, in accordance with the aforestated patent applications.
The object of the present invention is to provide a circular knitting machine which does not use vertically moving jacks 4 and instead effects selection directly on the needles.